The properties of two different "prion-strains" will be compared by physical measurements. Although a wealth of data suggests the absence of an essential nucleic acid component for infectivity, the existence of scrapie-strains, which are identified by characteristic incubation times, was always taken as an argument in favor of a nucleic acid component. Because of this enigma it is the aim of the project to find out whether the strains differ in the properties of the scrapie form of the prion-protein (PrPSc), possibly different conformations, or a second component is responsible for strain specificity, the obvious candidate being a nucleic acid. Two complementary approaches will be followed: 1) Employing the technique of return refocussing gel electrophoresis which has been developed earlier in our laboratory, size and content of nucleic acids in highly purified preparations of two prion-strains will be determined quantitatively. Combining those data with the results on the incubation times of the strains when determined after several steps of nucleic acid degradation, the dependence of strain-specific incubation times upon the presence of nucleic acids will be clarified. If such a dependence would be found, it will be searched for the corresponding nucleic acid molecule by particular hybridization procedures, and the conjectured nucleic acid will be characterized by techniques from molecular biology. ii) The properties of whole prions will be studied by physical techniques, in particular by searching for differences between the two strains. Because of the insolubility of prions in aqueous buffers novel approaches have to be applied. On the basis of earlier experience in our laboratory thermodynamic, optical absorption, and fluorescence measurements on prions in liposomes and detergent-lipid-protein complexes (DLPC), and the application of temperature-gradient gel electrophoresis to prions dispersed in DLPC appear most promising.